We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner-Freedman window. We show that is possible to derive a universal formula for the speed of sound for any theory. As an example we find all the planar black holes of the single scalar field consistent truncation of type IIB that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. We find the speed of sound for different values of the induced vacuum expectation value when a double trace deformation is induced in the gauge theory. For any theory, we show that the speed of sound is not bounded by any special value.